1. Field of Invention
This invention pertains generally to angular rate sensors and, more particularly, to an electronically configurable circuit for actuating and processing signals in a vibratory rate sensor.
2. Related Art
In a vibratory rate sensor or gyroscope, a mass is driven to vibrate or oscillate along a drive axis. Rotation of the sensor about an axis perpendicular to the drive axis causes a Coriolis force to be applied to the mass along a response axis which is perpendicular to the drive and sensing axes. The force is proportional to the product of the rate of rotation and the velocity of vibration, and the rate of rotation is determined by monitoring the force or the movement of the mass along the response axis.
Different types of sensing elements are used in such devices. Some are fabricated from silicon wafers, and others are fabricated of crystalline quartz and other piezoelectric materials.
With silicon sensing elements, the masses are commonly driven electrostatically, and the Coriolis induced forces are monitored capacitively. Such structures are generally planar, which tends to maximize the capacitance of the sensing elements.
Piezoelectric rate sensors are commonly in the form of tuning forks having at least one pair of tines which are positioned side-by-side and driven out of phase with each other in the plane of the tines. When the tuning fork is rotated about an axis parallel to the tines, the Coriolis force produces a second (pickup) mode of oscillation in which the tines vibrate in an antiphase manner perpendicular to the plane of the tines. Examples of such rate sensors are found in U.S. Pat. Nos. 4,654,663, 4,899,587, 5,396,144, 5,408,876, 5,585,561 and 6,262,520.
The tuning forks in such rate sensors often have more than one pair of tines, e.g. two pairs of tines arranged in an H-shaped configuration, with one pair being driven in the plane of the fork. The out-of-plane vibration produced by the Coriolis force is torsionally coupled to the other pair of tines, and the two pairs vibrate out-of-plane in opposite directions in the pickup mode. With a central mounting point, the out-of-phase motion of the two sets of tines cancels pickup mode forces at the mounting point, minimizing the effect of boundary conditions at the mount on the pickup mode oscillation.
Regardless of the type of sensing element employed, all rate sensors require certain common elements of electronic circuitry in order to function. Vibratory sensors require an oscillator circuit to produce the primary mode of vibration, and the output of the sensor must be detected, amplified, filtered and/or otherwise processed.
In addition to these common features, the electronic circuitry must also meet the individual requirements of a particular sensing element or type of sensing element. The resonance frequency of different types of vibratory rate sensors can, for example, vary widely even within a given class. Drive mode resonant frequencies can range from about 6 KHz to 40 KHz, and the strength of the output signal derived from the various devices can vary over a wide range, depending upon their size and efficiency. Output noise and bandwidth requirements also vary considerably.
In safety-critical applications such as automobile stability controls, built-in fault detection is also highly desirable. However, variations among sensors can make fault detection difficult since it depends, inter alia, upon the range and sensitivity of the sensor.
Heretofore, the variation among sensors has required specially adapted circuitry for driving and processing the signals produced by different types and sub-types of sensing elements. This has generally required either a unique integrated circuit for each type or sub-type of sensing elements or a multitude of external components which must be modified to configure an integrated circuit for use with a particular sensing element.